The Danish 1905 cohort: A genetic-epidemiological nationwide survey

Objectives: The authors studied nonagenarians, a rapidly growing age group whose cognitive and physical abilities have yet to be investigated systemat ically. All Danes born in 1905 were invited to participate in a home-based 2-hour multidimensional interview, including cognitive and physical perform ance tests and conection of DNA, carried out by lay interviewers. Populatio n-based registers were used to evaluate representativeness. Results: There were 2,262 participants, A total of 1,632 (72%) gave a DNA sample. Particip ants and nonparticipants were highly comparable with regard to marital stat us, institutionalization, and hospitalization patterns, but men and rural a rea residents were more likely to participate. Six months after the survey began, 7.2% of the participants and 11.8% of the nonparticipants had died. Discussion: Despite the known difficulties of conducting surveys among the extremely old, it was possible to conduct a nationwide survey, including co llection of DNA, among more than 2,000 fairly nonselected nonagenarians usi ng lay interviewers.